Thermally Stable Merocyanine Form of Photochromic Spiropyran with Aluminum Ion as a Reversible Photo-driven Sensor in Aqueous Solution

A reversible photo-driven sensor for aluminum ions based on photochromic spiropyran was reported with rapid response time. The detection of aluminum was performed via the chelation of aluminum ions with the merocyanine form (MC) of photochromic spiropyran. (1)H NMR studies confirmed the conversation from the MC form into the Al(3+)-MC form. Addition of aluminum ions to the spiropyran (SP) in a MeCN/H(2)O mixture results in obvious color changes with a loss in absorbance at 539 nm and an enhancement in absorbance at about 420 nm after irradiation at 365 nm. The metal chelation complex (Al(3+)-MC) can also be converted into the original SP form by irradiation with visible light. Aluminum ions can be detected down to 0.5 μM levels in a fast response of less than 5 seconds with no interference from other ionic species.